The interaction of airflow with an airframe's protrusions and cavities creates airframe noise. While engine noise dominates aircraft noise at takeoff, the airframe noise created by landing gear is a substantial contributor to approach noise for many aircraft. During approach, an aircraft engine is operating at less power than that during takeoff. Hence, the noise from the airframe is comparable to that of the engine noise.
The landing gear of commercial aircraft represent a complex system of wheels, axles, trucks or bogie beams, brakes, cable harnesses, torque links, braces, structure interfaces and wheel hubs. Skilled landing gear designers traditionally have emphasized the operational parameters attendant to proper deployment, operation and retraction of landing gear, and have not previously been directed to address noise attenuation as a design priority. While various noise reduction designs are known for fixed landing gear noise attenuators for deployable landing gears are less developed.
There is a need for retractable landing gear attenuation structures that successfully reduce noise emanating from the landing gear acoustic signature. The complexity of non-acoustical constraints on the design of landing gears have not permitted effective and practical noise minimization designs.